I think you nailed it you have a bad keyboard unit!
I would look at the TouchBar power rails, I’m suspecting one is being shorted out when you tighten the keyboard screws. The other possibility is you are a long screw when a short screw should be.
Look at the old keyboard mounting points to see if the new one matches exactly the same exposed areas where the mounting screws are located.
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Given the difficulty I prefer to replace the full uppercase assembly.
I think you nailed it you have a bad keyboard unit!
I would look at the TouchBar power rails, I’m suspecting one is being shorted out when you tighten the keyboard screws. The other possibility is you are a long screw when a short screw should be.
Look at the old keyboard mounting points to see if the new one matches exactly the same exposed areas where the mounting screws are located.